The invention relates to magnetic disks and more particularly to controllers for regulating the application of magnetic heads to the disks.
In a typical previous disk drive machine, the magnetic head is held off of the disk by a spring. An electric solenoid is energized, when desired, to overcome the spring force and to bring the head into contact with the disk. If the disk is of the type encased in a protective jacket, such as is disclosed in U.S. Pat. No. 3,668,658, the machine also may include a pressure member which is actuated by the solenoid to clamp the disk-jacket assembly to hold it in a correct predetermined plane for reliable data transfer. When the system is correctly electrically rated to handle tolerances of the head-solenoid connections and this additional task of compression of the disk-jacket assembly, the solenoid rapidly accelerates the head toward the disk. It has been noted experimentally that the rate of magnetic oxide erosion on the surface of the disk contacted by the magnetic head is very sensitive to and increases with the head impact velocity.
In many such systems, the head is loaded onto the disk at the same place, time after time. This loading, for the most part, is not done intentionally but occurs due to other requirements on the system. This may be under the control of a so-called index pulse which occurs at a particular rotative position of the disk, or such application of a head to a particular place on a disk may also be in response to other information derived from the disk during its rotation. This particular place of head application thus shortly becomes unduly worn.